Marine Science Faculty Publications

Rare Earth and Yttrium Phosphate Solubilities in Aqueous Solution

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Rare earth and yttrium phosphate solubility products range over more than 1 order of magnitude. Minimum solubilities are observed for light rare earths between Ce and Sm. For the elements Ce, Pr, Nd, and Sm solubility products (log Ksp0 (M) = log ([Mi3+] [PO43−])) at zero ionic strength and 25°C can be approximated as log Ksp0,(M) = −26.3 ± 0.2. Rare earth phosphate solubility products for well-aged, coarse precipitates increase substantially between Sm and Lu, with log Ksp0(Lu) estimated as −24.7. The solubility product of Y is similar to that of Ho (log Ksp0 (Y) = −25.0) and is much higher than those of all light rare earths. The solubility product of La is substantially larger than that of Cc (log Ksp0(La) − log Ksp0 (Ce) ≈ 0.5). Solubility products are strongly dependent on the conditions of solid phase formation. Fresh precipitates are much more soluble than slowly formed, well-aged, coarse precipitates. The pattern of rare earth and yttrium phosphate solubility products is generally similar to the fractionation patterns which are developed during phosphate coprecipitation.

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Geochimica et Cosmochimica Acta, v. 61, issue 8, p. 1625-1633